The present invention relates to an oxide composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities (generally referred to as “IGZO”; and the term “IGZO” will be used in the ensuing explanation as appropriate), and particularly relates to an IGZO sintered compact and a sputtering target formed from such IGZO sintered compact.
Conventionally, α-Si (amorphous silicon) has been used for a TFT (thin film transistor) as a backplane of an FPD (flat-panel display). Nevertheless, sufficient electron mobility cannot be obtained when using α-Si. Thus, in recent years, research and development of TFT using an In—Ga—Zn—O-based oxide (IGZO), which has higher electron mobility than α-Si, is being conducted. In addition, a next-generation high-performance flat-panel display using IGZO-TFT has been partially been put into practical application, and is attracting attention.
An IGZO film is generally deposited by sputtering a target which is prepared from an IGZO sintered compact. The IGZO sintered compact includes a sintered compact having a (111) composition of In:Ga:Zn=1:1:1 (atomic ratio). Nevertheless, this sintered compact having a (111) composition has problems in that the growth of crystal grains is fast and, therefore, the adjustment of the grain size is difficult. When the crystal grain size becomes too large, cracks tend to be generated at the crystal grain boundary, and the strength of the sintered compact will considerably deteriorate.
Patent Documents 1 to 6 basically describe that, in an IGZO sintered compact having a (111) composition, the flexural strength of the sintered compact can be increased based on unique sintering methods. Specifically, in the case of using a microwave heating furnace or an electric furnace with a general-purpose resistance heater, the growth of crystal grains is inhibited and the flexural strength is increased by drastically shortening the sintering time to 1 to 2 hours. Nevertheless, the microwave heating can achieve rapid heating or short-time sintering, but there are problems in that uneven heating may arise due to local heating, and the size of the sintered compact is restricted due to the limitation in the size of the furnace, and thus this is unsuitable for mass production. Moreover, when the sintering time is drastically shortened with an electric furnace, the growth of the crystal grains can be suppressed, but the structure may become uneven between the surface part and the inside of the sintered compact, the sintered compact may be subject to warping or strains more easily, and this may lead to the considerable deterioration in the yield.
Moreover, an IGZO sintered compact is required to have a sufficiently low bulk resistance to enable stable DC sputtering. Generally speaking, when the bulk resistance is high, DC sputtering becomes difficult, and, even if DC sputtering is possible, high power needs to be input in order to attain a practical deposition rate. Furthermore, when the bulk resistance is high, the probability of the generation of an abnormal discharge will increase, and there are problems in that this may lead to an adverse effect on the film caused by the generation of particles, and the occurrence of cracks or fractures of the sputtering target. Note that the Examples in Patent Documents 1 to 6 describe that deposition was performed via DC sputtering, but there are no specific descriptions concerning the bulk resistance of the sintered compact.